1/*
2Redistribution and use in source and binary forms, with or without
3modification, are permitted provided that the following conditions are met:
4
5    * Redistributions of source code must retain the above copyright
6    notice, this list of conditions and the following disclaimer.
7
8    * Redistributions in binary form must reproduce the above copyright
9    notice, this list of conditions and the following disclaimer in the
10    documentation and/or other materials provided with the distribution.
11
12    * Neither the name of "The Computer Language Benchmarks Game" nor the
13    name of "The Computer Language Shootout Benchmarks" nor the names of
14    its contributors may be used to endorse or promote products derived
15    from this software without specific prior written permission.
16
17THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
18AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
19IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
20ARE DISCLAIMED.  IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
21LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
22CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
23SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
24INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
25CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
26ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
27POSSIBILITY OF SUCH DAMAGE.
28*/
29
30/* The Computer Language Benchmarks Game
31 * http://shootout.alioth.debian.org/
32 *
33 * contributed by The Go Authors.
34 * based on pidigits.c (by Paolo Bonzini & Sean Bartlett,
35 *                      modified by Michael Mellor)
36 */
37
38package main
39
40import (
41	"flag"
42	"fmt"
43	"math/big"
44)
45
46var n = flag.Int("n", 27, "number of digits")
47var silent = flag.Bool("s", false, "don't print result")
48
49var (
50	tmp1  = big.NewInt(0)
51	tmp2  = big.NewInt(0)
52	tmp3  = big.NewInt(0)
53	y2    = big.NewInt(0)
54	bigk  = big.NewInt(0)
55	numer = big.NewInt(1)
56	accum = big.NewInt(0)
57	denom = big.NewInt(1)
58	ten   = big.NewInt(10)
59)
60
61func extract_digit() int64 {
62	if numer.Cmp(accum) > 0 {
63		return -1
64	}
65
66	// Compute (numer * 3 + accum) / denom
67	tmp1.Lsh(numer, 1)
68	tmp1.Add(tmp1, numer)
69	tmp1.Add(tmp1, accum)
70	tmp1.DivMod(tmp1, denom, tmp2)
71
72	// Now, if (numer * 4 + accum) % denom...
73	tmp2.Add(tmp2, numer)
74
75	// ... is normalized, then the two divisions have the same result.
76	if tmp2.Cmp(denom) >= 0 {
77		return -1
78	}
79
80	return tmp1.Int64()
81}
82
83func next_term(k int64) {
84	y2.SetInt64(k*2 + 1)
85	bigk.SetInt64(k)
86
87	tmp1.Lsh(numer, 1)
88	accum.Add(accum, tmp1)
89	accum.Mul(accum, y2)
90	numer.Mul(numer, bigk)
91	denom.Mul(denom, y2)
92}
93
94func eliminate_digit(d int64) {
95	tmp3.SetInt64(d)
96	accum.Sub(accum, tmp3.Mul(denom, tmp3))
97	accum.Mul(accum, ten)
98	numer.Mul(numer, ten)
99}
100
101func printf(s string, arg ...interface{}) {
102	if !*silent {
103		fmt.Printf(s, arg...)
104	}
105}
106
107func main() {
108	flag.Parse()
109
110	var m int // 0 <= m < 10
111	for i, k := 0, int64(0); ; {
112		d := int64(-1)
113		for d < 0 {
114			k++
115			next_term(k)
116			d = extract_digit()
117		}
118
119		printf("%c", d+'0')
120
121		i++
122		m = i % 10
123		if m == 0 {
124			printf("\t:%d\n", i)
125		}
126		if i >= *n {
127			break
128		}
129		eliminate_digit(d)
130	}
131
132	if m > 0 {
133		printf("%s\t:%d\n", "          "[m:10], *n)
134	}
135}
136